/Engine/Source/Editor/ViewportInteraction/Public/ViewportInteractionTypes.h
Finds the center handle count and facing axis index. The center handle count is simply the number of axes where the handle would be centered on the bounds along that axis. The facing axis index is the index (0-2) of the axis where the handle would be facing, or INDEX_NONE for corners or edges. The center axis index is valid for edges, and defines the axis perpendicular to that edge direction, or INDEX_NONE if it's not an edge
void GetCenterHandleCountAndFacingAxisIndex ( int32 & OutCenterHandleCount, int32 & OutFacingAxisIndex, int32 & OutCenterAxisIndex ) const